Cable TV systems, also known as Community Access Television (CATV) Systems, have evolved from simple broadcast systems for television services to bi-directional broadband networks which can carry voice, video and data traffic. This evolution has been accomplished in part by upgrading traditional cable networks to Hybrid Fiber Coaxial (HFC) networks which utilize fiber optic systems in conjunction with active electronics and coaxial cables to deliver broadband signals to the home. These networks also support the reception of return path signals, which are signals generated by units in or near the subscriber and which send data or voice signals from the subscriber or business location to the network through the cable system.
By providing advanced telecommunications services over HFC networks, network operators can enhance their service offerings to include voice, Internet access, and other new and unique multimedia services. Although some of these services may have minimal requirements for the transmission of data from the residence to the head-end and the network, many applications require the reliable transport of data and, in fact, need to have guaranteed and reliable bandwidth.
For example, voice communications can be carried over an HFC network based either on traditional circuit switched technology or emerging Internet Protocol (IP) standards. In either of these transport modes, an unreliable and noisy return path can cause degradation in service and even loss of an active call.
Because the configuration of the cable system is multipoint-to-point from the subscribers to the head-end, the return path has the undesirable characteristic of accumulating or “funneling” noise towards the head-end. The number of subscribers connected to the network is typically greater than 500, and many subscribers can have power dividers (splitters) installed in their homes to allow connection of multiple settops to the cable network. The result of the large number of subscribers and the multiple connections in the home is that there are a large number of points on the cable network where undesirable signals can enter the return path. The commonly used term for undesirable signals on the cable return path is ingress. Ingress is typically, but not limited to, AM shortwave broadcast signals and industrial and atmospheric noise, which can enter on the drop cable connecting the subscriber to the cable plant connection termed the tap, and via the coaxial wiring in the subscriber residence or business location. The coaxial wiring used in the home may be of low quality, and will allow ingress because of the low amount of shielding provided with respect to high quality coaxial cable which has a dense braided wire shield which provides high isolation of the center conductor from external electromagnetic fields. The coaxial wiring in the home is also typically unterminated, and can act as an antenna since currents generated on the outside of the shield can to some extent couple to the inside of the shield at the unterminated end and subsequently excite the center conductor. The accumulation of noise on the return path has adversely limited the use of the return path for many purposes.
For the foregoing reasons, there is a need for a method and apparatus to detect ingress and attenuate it at or near the subscriber location.